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A ril 21, 1959 P. GRAHAM 2,882,604

GRAPHIC MACHINE Filed June 29, 1953 "(Ill 3 Sheets-Sheet 2 2- IIIIIII Afforney April 21, 1959 P. GRAHAM 2,882,604

' GRAPHIC MACHINE Filed-June 29 1955 s Sheets-Sheet 3 FIG. l4

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14 fiarney United States PatentC GRAPHIC MACHINE Phillip Graham, Pittsburgh, Pa. Application June 29, 1953, Serial No. 364,674

13 Claims. (Cl. 33-76) This invention relates to a graphic device which is useful, in general, as a guide for aiding in engineeringdrawing work, template making, sheet metal fabricating layout work, and the like, so as to quickly and accurately measure and draw straight lines at various pitches or slopes.

The graphic device of the present invention, in gen eral, is similar to a carpenters square and the L-shaped square formed by the two scaled legs of a conventional drafting machine. It may be clamped securely against the edge of a T-square or other types of straight-edge guides so as to prevent it from slipping out of a true tilted position. The present graphic device is more useful than conventional drafting machines, triangles, and conventional protractor equipped triangles and L-shaped squares, since it is more flexible in that it may be more readily set-up so that it may be used intermittently at various tilted or horizontal selective positions and with quickly interchangeable scales that are required in this type. of graphic work. It has an indexed arrangement for setting up all the angles or pitches required for a given job and indicating clearly the degree of slope of all these angles.

Other types of conventional drawing devices must be frequently reset to various angles or pitches by slow and tedious operations. Other similar conventional L- shaped square graphic devices do not have the index for numerous pitches or angles or the clamping means, and it 'is diflicult to hold them in a true position.

The graphic device of the present invention, briefly stated, allows positioning, by means of a reciprocating movement, to give .left and right handed sets of angles or slopes with the same index setting; that is, a set comprising an angle and the angle complementary to it (90 difference). Some conventional adjustable triangles that are widely used can, by a single setting of a protractor. give an angle and an angle complementary to it,'but cannot be positioned to the opposite set as quickly and with as little motion as can my graphic device. These conventional adjustable triangles do not have a means to readily show which angle or bevel on the triangle is that indicated by its protractor. Thus it is diflicult to determine the proper side for a given angle with conventional adjustable triangles when they are set at nearly 45. These conventional adjustable tri-' angles have no means to allow quick and accurate indexing for various bevels or angles. They have no suitable interchangeable scales; and they have no clamping means for fastening them to a T-square, thus they are very limited in their usefulness as an aid to rapid and accurate drawing. v

There are conventional graphic devices of the type which may be flopped over'on its opposite face to give left and right hand sets of angles, but this takes more movement and time than is required with my graphic device. Also they do not have a means to setup and index groups of angles for intermittent use as 2,882,604 Patented-Apr. 21, 1959 means to clamp them .to the T-square, nor do they have interchangeable scales. Thus they have very limited use.

Large conventional drafting machines cannot be setup with a group of angles indexed to furnish left and right hand sets of these angles and the angles complementary to them.

Persons that are handicapped by a crippled arm or hand may use the present graphic device to advantage; whereas it is diflicult for them to use the conventional adjustable triangles, or the like, or the conventional triangle to triangle drafting technique for drawing sloping lines. With the latter technique, the draftsman holds the two triangles and slides one against the other to position them for drawing sloping lines parallel to an adjacent existing sloping line. Even with two good hands it is diflicult to keep the triangles from slipping out of position or alignment.

With my graphic device, the draftsman can readily position the device with one hand due to the simple index operation and the clamping means, while he maintains pressure on the T-square or straight edge with his arm toprevent it from slipping.

With conventional protractor-equipped similar devices that have to be set every time a change is made from one set of angles to another, much time is spend on frequent resetting of angles and in adjusting them to exactness. This time consuming operation is considered so objectionable for drawing occasional sloping lines that many draftsmen prefer the quicker sliding triangleto-triangle technique.

- with my graphic device, the angles are .set up in the index only once, and then they can be used intermittently with other angles without losing their accuracy.

The basic advantage of my graphic device is its flexibility to quickly and accurately measure and draw all straight lines for a complicated sketch with one set-up. The graphic device requires less skill to operate than do similar instruments. It is not as cumbersome as some of the more useful conventional graphic machines. It takes less effort to operate since it is low in weight and requires less movement by the operator to draw a group of lines than with other similar devices. It combines, into one flexible instrument, all the functions of conventional triangles, scales, and protractors, plus improvements that overcome the objectionable features of these conventional instruments.

:An object of my invention is to provide a novel and useful graphic device for engineering drawing or drafting, template making, and fabricating shop lay-out work.

and the like. There are exceedingly simple operations with this device which allow accurate and rapid measuring for and drawing of straight lines, including socalled horl-' zontal lines, vertical lines, and sloping lines of various selective angles or pitches which may be all set-up for quick indexing when they are to be used frequently on a a given job. My graphic device allows indexing of selective are usuallyrequired for a given job. They have 'no angles, which automatically also furnishes the comple mentary angles; and this set of angles may be quickly switched to either a right hand or a left hand arrangement, or opposite slopes. One of these indexed set-ups will give four bevels or angles, plus the horizontal and vertical positions; and the horizontal lines may be selectively scaled from right to left or from left to right. There is a means to clamp this graphic device to a T-square to keep it from" being moved out of its true position.

Another object of my invention is to provide a graphic device which is readily attachable to a conventional drafting machine so as to enable the machine to be used to selectively measure and draw more rapidly and accurately. Other objects and advantages of my invention will be come apparent from a study of the following description thisinvention, positioned thereon in one of its many working positions.

Figures IE to 1F, inclusive, show fragmentary plan views of a drawing board with the graphic device illustrated in some of the possible positions other than that shown in Fig. 1A.

Figure 2 is an enlarged fragmentary plan view with the graphic device positioned the same as in Fig. tA, show ing in detaii some of the principles of the graphic device embodied in this invention.

- Figure 3 is an enlarged fragmentary sectional elevation taken along line 3-3 of Fig.2.

Figure 4 is an enlarged fragmentary sectional elevation taken along line 4-4 of Fig. 2.

Figure 5 is a fragmentary sectional elevation taken along line 5-5 of Fig. 2.

Figure 6 is an enlarged fragmentary sectional elevation taken along line 6-6 of Fig. 2.

larged plan view Fig. 2, which is similar to Fig. 1A,

Figure 7 is an enlarged fragmentary sectional elevation taken-along line 7-7 of Fig. 2.

I Figure 8 is an enlarged fragmentary plan view taken along line 8-8 of Fig. 5.

Figure 9 is a sectional elevation taken along line 9-9 of Fig. 8.

. Figure 10 is a fragmentary sectionai elevation taken along line 10-10 of Fig. 8.

Figure 11 is a fragmentary sectional elevation taken along line 11-11 of Fig. 8. 3 1

Figure 12 is an enlarged detail of a typical pin used on this graphic device.

Figure 13 is a fragmentary sectional elevation similar to Fig. 5, but showing the index arm reversed from the position shown in Fig. 5.

Figure 14 is a plan view showing a modified method of using this graphic device by suspending it from a swiveled arm.

Figure 15 is a plan view showing a modification of the graphic device used in conjunction with parts of a conventional drafting machine.

Figure 16 is a plan view showing a further modification of the graphic machine used in conjunction with a conventional drafting machine.

Figures l7 and 18 are plan views showing modifications of the graphic device, using modified conventional drafting machine scales in the construction.

Figure 19 is a plan view showing a modification of the graphic device which has a single tilted edge.

Figure 20 is a plan view showing a modification of the square graphic device.

Figure 21 is a plan view showing a modification of the graphic device in the form of a triangle.

Referring more particularly to Fig. 1A, the drawing board 1 has a T-square 2 on top of it. A conventional so called parallel straight edge may be used in place of the T-square. The board 1 may have a slot along the left hand side which forms a track for a removable pin in the T-square 2. This slot and pin arrangement prevent the T-square from moving out of alignment, see Fig. 14. The square Q, which embodies many of the principles that are new and useful, is shown attached to the T-square 2. The square Q is shown tilted to enable an engineering draftsman, template maker, or the like, to readily draw sloping lines. The lines are generally drawn along the inside edges of the square Q. The tower structure sketch 3 is drawn with the aid of the square Q.

Figs. 1B, 1C, 1D, 1E, and IF show the square Q in some other tilted and non-tilted positions that may be used to aid in drawing the sketch 3. The square Q may be inverted and be used against the opposite or near edge of the T-square 2 (not shown) if the draftsman prefers that arrangement. As can be seen in the enthe sketch 3 is a line diagram of a tower structure, which is a typical elevational view for structural steel plans. The left and right hand tower legs have the same slope. The slope is also called the angle, bevel, or pitch, in structural drawing work. The tower sketch 3 is, in general, symmetrical about its center except for the splices of the three tiers of bracing and the dimension lines, which are given on one leg only, for example. The sketch 3 has various length lines at various slopes. They are the horizontal and vertical lines, three sets of diagonal bracing lines having different bevels or slopes, and the tower legs which have another slope. All the slopes are both right and left hand. When the engineering draftsman makes shop detail drawings of such a steel tower, he must draw hundreds of structure lines, dimension lines, extension lines, and guide lines for lettering, etc., in these various slopes. A large tower may require many drawings, 24 inches by 36 inches, usually drawn to one inch scale equalling one foot; so; by using the square Q to aid in accurately and speedily measuring and drawing these lines, accurate work on large jobs can be made quickly at low cost. The draftsman has to draw a little bit here and there to create a shop 'detail'sketch, etc., thus this type of drawing-work has a sequence which causes frequent changing ofdrawing procedure from one set of angles to another,'as

well as horizontal and vertical. Conventional drafting with equipment using a pro-' is changed to draw sloping lines, other than that of the complementary angles with some devices, except that they usually have an index for positioning to zerodegree, degrees, 30 degrees, and 45 degrees.

The square Q has an index arm N1 which is used'to hold selective units with pins for tilting the square Q; This arrangement allows the operator to set-up this square Q for obtaining and maintaining all the angles, or slopes that are to be used for drawing the tower. sketch 3. Once the squareQ is set-up, there are simple operations to be made by the workman to change the position back and forth for various sets of angles and: to the horizontal and vertical positions, as will be described fully further on.

The square Q has a body or frame 4. The frame 4. has legs 4d and 4e, also pin arms 4a, 4b, and 4c which have holes to take pins 5a, 5c, and 5d, which may besimilar to the pin 'Sb shown in Fig. 12. These pins and pin 5b are positioned so they may be made to bear against the edge of the T-square 2 to adjust the square Q to various tilting positions; they also are the means. used to pivot or rock the square Q to these various positions. Normally, the pins 5a, 5c, and 5d are inserted fully as shown in Fig. 4 and allowed to remain in that position. They may be raised to the position Sca, shown in Fig. 4, to allow disengaging of protractor-clamps from the square Q. r The protractor-clamps C1, C2, C3, and C4, whichare alike, are engaged by the pins 5a, 5b, 5c, and 5d.-

These protractor-clarnps are slidable along the straight tion. A typical clamp C1 is shown in enlarged elevation Fig. 4; itis a self-aligning and self-coupling clamp;

the clamps will be described in detail further on.

The pins 5a, 5c, and 5d may be fixed permanently to the arms on the frame 4, and to the clamps C1, C2, and- C4, if it is desirable.

When for limited operations none of the protractor-l clamps C1, C2, and C4 is to be used, pins 5a, 50, and;

5d may be used without them, or the pins may be omitted; and the outside corners of the frame4 may be:

used as the bearing points. This positioning without pins a, 50, and 5a is indicated in Figs. 4, 6, and 7 by the dot-dash outline position 2a of a fragment of the relocated T-square 2.

The square Q may have the magnetic clamps 29a, 29b, and 29c in the frame 4, which are pieces of mag ne'tized metal such as Alnico. They may be used to hold the square Q to the T-squ'are 2. The edge of the T-square 2 would have a strip of iron to work with the magnetic clamps. These magnetic clamps prevent the square Q from pulling away from the straight edge, while they allow it to he slid alo'ng'the edge.

The pins may all be alike so as to be interchangeable; They are threaded almost their full length for engaging the pin arms and the pin holders H1, etc. The pin ends engage plain close fitting holes in the protractor-clamps C1, etc. The pins may be bowed slightly when made of resilient material so they will fit tightly in pin arms. The pins may also be magnetized to bind them to engaging parts of steel. Aresilient wire 25 extends through clamp C1, as shown in Fig. 4. This wire 25 springs aside into a suitable groove in the protractor-clamp when a pin is inserted or removed. This Wire 25 acts as a key to fitin the keyway-like groove near the bottom of the pin, to hold the pin and the protractor-clamp to gether. The clamps C1, C2, C3, and C4 and the arms 4a, 4b, and 4c may have hardened sleeve inserts for preventing wear and tear from the pin action.

The T-square 2 may be used as T-squares are normally used, that is, it -may be :pushed up and down the drawing board 1 and the square Q may be kept against the T-square and be slid with'it and then along its length. The square Q may also be disengaged from the T-square and moved independently to a desired position along the T-square. The ends of the frame legs 4d and 4e are beveled at about 45 degrees so that the square Q may be tilted to 45 degrees in arrangements similar to that shown in Figs. 1B and 1E.

As shown in Fig. 3, the transparent frame edging 4h is beveled on the top to allow a suitable working edge for drawing. A fragment of a conventional pencil 6 is shown by a dot-dash outline. The frame '4 may be made of light weight suitable materials such as plastic or aluminum. It is highly desirable to have transparent working edgings 4h and 4k, so that the draftsman may see how close he is drawing to adjacent lines that are below the edgings. If the frame 4 is made of clear plastic, frame 4 and edgings 411 and 4k may be combined and be made of one piece.

The inside edge of the square Q has the scale assemblies S1 and S2; assembly S1 is shown below the edging 4h in Fig. 3. These scales may be of transparent plastic. The edging 4h is shown recessed to receive the scales. It offers protection to prevent damage to the scales, and the recesses would keep the scales in alignment. If the frame 4 and the edgings are made of aluminum or other opaque materials, the scales may be located on the top of the edging 4h in the position Sla, shown by a dot-dash outline in Fig. 3. When the square Q is to be used only with one set of scales, such as full size scales for template making and shop work, the scales may be marked on the top of opaque frames or edgings. Such full size scales may bemarked on the bottom or the top of a transparent frame edge. An opaque frame with opaque edgings may be modified from that section shown in Fig. 3 so as to allow the transparent scales to project out further from the frame edgings 4h and 4k. As can be seen in Fig. 3, the scale assembly S1 has a roughened reinforcement wire 26 at its center. As the plastic scale 27 would likely have a high coeflicient of expansion, the wire 26, with a low coefficient of expansion, is used to restrain the plastic from expanding or contracting excessively in length. Thus the reinforced s'cale does not cause inaccuracies in measuring. The wire 26 maybe sandwiched between two pieces of plastic that are 'fasfelted together to form the base of the scale, or a single strip of plastic 27 may be used with the reinforcing wire -26 imbedded in it. The scale markings may be made with a photographic process. The photographic repro= duced markings may be made at low cost in suitable colors or in black and white. Small balls are attached to the ends of the wires 26 so that the scales S1 and S2 may be detached or attached quickly and accurately to the square Q. These balls would fit into suitable sockets cast into the frame or edging at the center. The balls at the outer ends of the scales may be held by {resilient clips 7, which keep the scales taut. These clips 7 are bent and have slotted openings to allow the bail ends of scales to be attached to them. The scales S 1 and S2 may be made so their graduations start at zero, where they meet at the center of the "square Q, and graduate out to their ends, so that measurements may be taken in two directions from the center from one position of the square Q. Conventional interchangeable drafting machine scales require a second positioning for sc'al'ing at a right angle to the first operation. In general, the scale assemblies S1 and S2 would be interchangeable with scales of other graduations. These scale assemblies are shown as having graduations on two edges so as to combine two different scales that are frequently used in one assembly, so they will be readily available when needed. They may be turned over quickly by 'unhooking the one end, flopping and rehooking the ball ends to change from one desired scale to another. 7

Conventional interchangeable drafting machine scales have tight fitting tapered sockets which make Scale changes a tedious, less accurate, and longer operation. Frequent changing of the scales is often required, "since the scale edges in working position may, for instance, be of one inch equals one foot; and -it becomes necessary "to frequently replace them with scales of 3 inches to a foot for making enlarged details or large layouts, before resuming with the detail sketching at one inch scale. A differently graduated scale in registry on leg 411 from that on leg 4e would be useful at times when a sketch, for instance, is drawn with a small scale for overall sizes and a larger scale for the details. The full size scales 4g along the outside edges of frame 4 "are convenient for miscellaneous measuring, such as for spotting the locations for sketches and for measuring guide lines for lettering, etc. Since the index arms block full use of these scales, they would be of little use except when index arms are removed. A modified square (not shown) with interchangeable scale assemblies similar to S1 and S2, attached along the outside edges of the square, would be useful when drawing and measuring horizontal vertical lines without the index arm attached.

The frame 4 may have template cutouts in the legs t'o facilitate sketching, such as spaced holes for the measuring of standard spacing and for templates for aiding in drawing standard parts, such as small circles, weldihg symbols, etc. Only three of these template cut-outs are shown. Others may be used to suit various branches of graphic work. The cut-outs shown are a circular template 14, a diamond template 14a for outlining the size of holes and rivets in structural steel work, and a series of spaced holes 14b for spacing lettering guide lines.

The pin 5b is held in the pin holder H1 (see Figs. 2 and 5), which is attached to the index arm N1 (see Figs 2 and 5). There is a means to accurately set the pin holder H1 so as to create an indexed location "to aid in quickly and accurately obtaining the desired tilted position for the square Q for a drawing operation at an angle or slope. This will be described in detail "further on. Other identical pin holder's H2, H3, and H4 are shown. They are all attached and selectively positioned to the index arm N1 for the various slopes or angles required for drawing the sketch 3. The pin 5b projects down, as does the pin 50, so that it can be made "to bear against the edge of the T-square 2. The pin "51: is

leg-4e of the square.

'7 eatcd at a position which is equidistant from the pins a and 50. With the pin 5c and the pin 5b bearing against the T-souare 2, as shown in Fig. 2, an angle or bevel is created between the T-square 2 and the bottom leg of the square Q. This tilt of the square Q creates the proper slopes for measuring and drawing the left hand leg of the tower shown in the sketch 3. The tower leg is drawn along the leg 4d of the square Q. The leg 4e of thesquare is sloped at an angle complementary to the angle created by the leg 4d. This sloping leg 42 is used in the drawing of the extension lines out from the left hand tower leg. so they suit the dimension lines that are drawn parallel with the tower leg. After the left hand leg of the tower in the sketch 3 is drawn, or partially drawn. the square Q may be pivoted or rocked on pin 5b until pin 51: bears against the T-square 2. This position is shown in Fig. 1B. It creates the same degree an les that were created in the arrangements shown in Fig. 1A and Fig. 2, except that they are opposite hand or reversed in respect to the legs of the square Q. With the set-up shown in Fig. 1B, the right hand leg of the tower can be measured and drawn along the leg 4d of the square; and any dimension lines can also be drawn along the leg 4:1, with extension lines or dimension lines being drawn at right angles with the Thus is can be seen that with the pin 5b indexed in index arm N1, the draftsman can drawthese two sets of slopes by quickly changing back and forth from one set of complementary slopes to another merely by rocking the square Q with the pin 5b bearing fagainst the T-square 2.

When the draftsman wants to draw the horizontal and vertical lines in the tower in the sketch 3, the pin 5b may be removed or raised so that it no longer engages the protractorclamp C3 and the T-square 2; or the index arm N1 may be removed temporarily if desirable, particularly while consecutively drawing a great many horizontal and vertical lines. The square Q is positioned as shown in Fig. 1C by rocking or pivoting it until the pins 5a and 50 both bear against the T- square 2. Then the horizontal lines can be measured and drawn along the leg 4e, and vertical lines can be measured and drawn along the leg 4d. The position of the square Q, as shown in Fig. 1C, is considered to be the most desirable arrangement for drawing vertical and horizontal lines by a right handed draftsman. It is similar to the conventional method of drawing horizontal lines along the upper edge of a T-square, and of drawing vertical lines against the left vertical side of a conventional drafting triangle. That method is widely used because it allows the draftsmans hand to maintain a natural position'while drawing. Since the square Q is used to measure and draw, it is highly desirable at times to pivot the square Q to the position shown in Fig. 1D, with the pins 5c and 5a hearing against the T-square 2. With this arrangement, the draftsman may measure and draw the vertical and horizontal lines from a common point when it is more suitable for the sketching being done. Thus it will be seen that even a right handed draftsman will use the square Q in the position shown in Fig. 1D to allow him to draw and scale at the same time, although he will have to twist his hand slightly from the conventional drawing position. A left handed draftsman would find the positions of the square Q as shown in Figs. 1D, 1E, and IF highly desirable for his technique.

-To use the square Q in the positions shown in Figs. 1E and IF, the index arm N1 is unhooked from the tram leg 4e, where it is hinged, and'is moved to the position shown by a dot-dash index arm outline N2 on the leg 4d. The square Q is tilted as shown in Fig. 1E, by having the pins 515 and 5d bear against the T-square 2. The draftsman, Wherether he is left or right handed, takes his choice whether he wants to use the square Q in positions such as that shown in Figs. 1A and 15 min the positions shown in Figs. 1E

and IF. All draftsmen would, at 'times,switch the index arm N1 to give the alternate arrangement when conditions would require it, such as when he is sketching near the ends of the T-square 2. The pin holders H1, etc., can be indexed in the index arm N1 to give up to a 45 degree tilt for the flat angles to the horizontal, which is all that is necessary, since the complementary angles on the other leg of the square give the steep angles to the horizontal, from 45 degrees to degrees.

Another index arm, identical to the index arm N1, may be used in the position N2. Either one or both of them may be attached at the same time, if so desired. In general, one would be removed to keep down the weight and to make the device non-cumbersome.

When the draftsman wants to draw the top set of bracing of the tower in the sketch 3, he removes the pin 5b from the pin holder H1, and inserts it in the pin holder H2, which has or is adjusted to give the proper angle or tilt. With this tilt, one diagonal brace and the dimension lines for it may be drawn against the leg 4e of the square Q; and the lines drawn to complementary slopes or angles would be drawn against the leg 4d of the square. After this operation, the square Q is rocked or pivoted on the pin 5b, against the T-square 2, to the opposite position. This. would allow the other top diagonal brace in the tower to be drawn. After the top set of bracing has been drawn, or partially drawn, on the tower 3, the pin 5b is removed from the holder H2 and inserted into the holder H3 until it projects far enough to allow it to bear against the T-square 2, then the middle set of diagonal bracing may be drawn or parts of it may be drawn. Then the pin 5b may be removed and inserted into the holder H4, so it can be made to bear against the T-square 2. Thus the square Q can be tilted to enable the draftsman to draw the lower set of the bracing on the tower 3.

Although I have referred to the pin 5b as being removed from the pin holder H1 and inserted in other pin holders, pins identical to the pin 5b may be inserted in the pin holders H2, H3, and H4 to make them quickly available. When not being used, these pins would be kept in a raised position, such as that which is shown by a dot-dash pin outline above the pin 5b in Fig. 5. They are raised enough to prevent them from engaging the protractor-clamp C3 or from bearing against the edge of the T-square 2. If a tower similar to that shown in the tower sketch 3 were to have more diagonal members,

or details of diagonal connections to adjoining parts,

more pin holders, similar to the holder H1, may be fastened and positioned to the index arm N1, or another such index arm, so as to provide all the required indexed angles. If so many indexed angles were required that they could not all be mounted on one or two index arms, additional index arms, similar to index arm N1, may be used for the over-flow. An index arm in position N2 may hold the additional indexed angles. Additional index arms may be kept within reach, with settings indexed for standard angles that are frequently required, such as angles varying by ten degrees for sheet metal pattern development, angles for spacing holes on a bolt circle in piping flanges, and the angles used on a standard pitched hip and valley roof type structural steel drafting job. When isometric sketches are frequently to be made, a 30 degree setting may be kept available along with other frequently used angles. The square Q, with a setting at 30 degrees and with an isometric scale, would aid in speedily drawing isometric sketches. When large sets of odd angles, such as those used for drawing hip and valley roof details are used frequently, a template 28 (see Figs. 9 and 10), may be used to more rapidly adjust the group of pin holders. A template 28 may be 'a thin strip of steel, with accurately located holes punched then the proper end hole in the template 28 is slipped absence over the sleeve 11b, where -it is held with magnetic attrac tion to magnetized frame 11 or by other means. The remainder of the pin holders may be quickly positioned 'by removing the worms 12 and sliding the holders along rack sections 9a and 9b, until their sleeves register with the holes in the template 28. Then the resilient hinged tops 11a are closed to lock the pin holder securely. The gear-like outer parts of the sleeves 11b in registry with the outer teeth on the racks, restrain the pins from tilting.

The open hinged connections of the index arms to the frame 4 enable quick interchanging of the index arms. The bracing hinges 8a, 8b, 8c, and 8d are alike. They are used for attaching the index arms such as the arm N1 to the square frame 4. The center hinges 8e and 8f are alike. Figure 6 shows a cross section of the hinge 8a. Figure 7 shows the bracing hinge 8b. These hinges may be fastened to the frame 4 with screws or they may be fastened by other means, such as by being inserted in a plastic frame 4 with suitable offsets on the hinges to engage the plastic.

The index arm N1 has a center assembly which is formed by two rack sections 9a and 9b which have rack teeth on each side of each section. These rack sections are shown enlarged in the details shown in Figs. 8, 9, 10, and 11. The ends of racks 9a and 9b, near the frame 4, are joined to a cross piece to help form the hinge arrangement with the hinge 8e as shown in Fig. 6. The other ends of racks 9a and 9b are joined to a cross piece 90. The bracing for the index arm N1 consists of the bracing wires 10a and 1%, which may be threaded and have nuts to allow for adjustment. These wires 10a and 10b pass through holes in the ends of the cross pieces 90. The other ends of the wires 10a and 10b are welded or otherwise fastened to the heavier bracin'g members 10c and 10d. The bracings 10c and 10d maybe welded or otherwise fastened to the racks 9a and 9b, and they may have ball-like offsets at their ends to engage the sockets in the hinges 8a and 8b. The index arm N1 is inserted from a vertical plane to allow it to fit into the hinges, then it is pivoted down into a horizontal position, which locks it in place. The index arm N1 may be raised and lowered, by pivoting, to nearly a vertical position without unhinging. The hinges are so designed that they can take the thrust that is made against them by the pressure on the square Q by the draftsmans pencil. The raised positions of the arm N1 are shown by the dot-dash outlines in Figs. 5, 6, and 7.

A converted arrangement is shown in Fig. 13 with the index arm N1 under-slung from the arrangement shown in Fig. 5. This arrangement cuts the error or play due to the pin tilting or bending, and thus increases the accuracy in drawing. It may be used to advantage with a thin T-square, such as those made of steel, when no protractor-clamp C3 is used. Highly magnetized pins may be used to magnetically clamp to such a thin steel T-square.

The index arms N1, etc., are so made that they may be 'pivotally raised to allow 'for various advantageous operations, such as when it is desirable at times to raise the index arm N1 to a vertical position to keep it out of the draftsmans working area. The pin 8g, shown in Fig. 6, is projected into the hinge into the arm N1 to restrain it from being lowered when it is so desired, or to keep the hinge in a lowered position. There are holes at right angles to each other in the end of the arm N1, which allows the pin 8g to be inserted to form a lock. The pin 8g and the hole in the hinge 8e may be threaded or the pin may be bowed (not shown), so that it fits tightly and thus it will not easily fall out or work loose.

The pin holder H1 is shown enlarged in Figs. -8, 9, 10, and 11 A bent plate frame 11 has a hinged top 11a. The frame 11'Inay be of steel and -'it'may be magnetized to hold template 28. The hinged top may be of "spring steel; and it may be bowed as shown by the raised posi- 10 t-ion that is shown by a dot-dash outline 112m in Fig. 9, so that it will be compressed in closing to make the pin holder mechanism tight fitting with the racks 9a and 9b. The hinged top 11a is forced down into the notched end of the frame 11, as shown in Figs. 8, 9, and 1 1. The notch to receive top 11a is sprung to allow a tight fit. The gear-like sleeve 11b has a tapped hole to suit the pin 5b. The gear toothed outer part of sleeve 11b engages the outer set of rack teeth on the rack 9b to prevent excessive play, and thus inaccuracies by forces that tend to tilt the pin holder H1. The outer teeth on rack 9a engage sleeve 11b when the arm N1 is underslung, as shown in Fig. 13. The rounded lower left hand edge of the rack 9a and the upper right hand rounded edge of the rack 9b are shaped to fit the frame 11, and to thus prevent the incorrect attaching of the pin holders H1, etc. The pin holders H1, etc., may be 'used to tie the racks 9a and 9b together to make them act together as a beam against lateral forces, even when they are not being used for indexing. The threaded worm 12 engages the inner teeth or parts of threads of the racks 9a and 9b. The worm 12, being a helix, has clearance for allowing it to be inserted between the racks 9a and 9b. It will ti-lt slightly out of line. The worm 12 has its ends counterbo'red to engage the top part of the bent arms 11g on the frame 11, thus restraining the worm 12 from disengaging when top 11a is open. The Worm 12 may be removed or inserted by springing the bent arms 11g. Square socket holes in the ends of worm 12 fit the square end of adjusting tool or pick 120. The ends of the worm 12 are toothed to allow it to be gripped with the forked end of the pick 120 (shown in Figs. 9 and 11), which is held by the workman, to turn the worm 12 to cause a Vernier adjustment in the positioning of the pin holder H1 along the length of the racks, or the square end ofpick 120 may be inserted into an end socket of the worm 12 and be turned for vernier adjustment. The sleeve 11!) is restrained from lifting when the pin 5b is lifted by the sleeve collar formed by spreading the base and by the hinged top 11a. The hinged top 11a has a slit in its end to allow a marked tab lid to be inserted. The top surface of the tab 11d indicates the fiat angle to the horizontal, and the lower surface of ta'b 11d indicates the complementary angle at which this particular unit is being indexed. This tab 11d may be an expandable piece of paper. The hinge top 11a is shown locked; the

open raised position of the top 11a is shown by the dot-' dash outline llaa. The indicator needles 112 and 11 register the tilt o-r angles on the protractor C3. The resilient lock 12a may be a piece of resilient rubber. It is held by an offset punched into the bottom of the frame 11. The resilient lock the Worm 12, which restrains it from creeping or turning from vibration. The pin holders I-Il, etc., are narrow to allow them to be set close together for indexing angles that are slightly different. The head of pin 5b is shown by a dot-dash outline in Figs. 9 and 10 as Fig. 8 does not include the vpin head. The pin 5b is inserted in the hole in the center of the sleeve 11b after the pin holder H1 has been clamped onto the rack sections 9a and 9b. The pin 5b and the sleeve 1111 may be threaded steeply to allow the pin to be quickly advanced, to thus allow it to be quickly inserted or removed with little effort and without jarring or moving the square Q and the T-square it may be clamped to.

A modified plain bowed pin 5b may be used to 'fit hole in the sleeve 11b. The square Q may be lifted by gripping a threaded pin 5b, and 'in doing so the pin may be turned to advance it further so it will project to allow it to bear against the T-square 2, either with or without the protractor-clainp C3. The threaded pin 5b may be turned in the opposite direction to raise it so it will no longerproject to engage the T-square 2 or the clamp C3. The threaded pins 5b, 5a, 5c, and 5d are less :likely to work loose bowed slightly than plain straight ."pins,

12a maintains pressure against especially when using the square Q- with a "sloping or vertically mounted drawing board 1. Threaded pins would allow one hand removal or insertion of the pins with little efiort; this would be particularly useful to handicapped workmen with one useful hand.

The protractor-clamps C1, C2, C3, and C4 may be used when it is desirable; and they may be omitted or disengaged by removing or raising the pins b, etc., when they are not being used. Some types of drafting work would not require the protractor-clamps C1, etc. Some types of work would not require the clamps but would make use of the protractors. Theclamps may be used to securely hold the square Q in an inverted position to the lower edge of a T-square 2 or a cable rigged parallel edge, particularly so on a vertical or steeply sloped drawingboard. The draftsman may raise the pins and slide the clamps aside until they are required again when the clamps are not useful for a particular sketching operation. The clamps C1, etc., hold the square Q to the T-square 2 when pressure on the edge of the square Q while drawing would have a tendency to tilt it. The clamps C1, etc., are slidable along the T-square even when clamped to it. The protractor-clamp C3 is shown enlarged in Fig. 4; the other clamps may be identical or similar to it. The protractor indicator needles 4} point to both the angles on the protractor for the set-up on the square, that is an angle and the complementary angle at right angles to it. Protractor part 13 of the protractor clamp C1, etc., may be made of such material as plastic or aluminum to keep the weight low; orthey may be magnetized metal, such as aluminum-cobalt-nickel, alloy such as sold under the trademark Alnico, to hold it to an iron edged T- square or other iron or steel edged guides. The protractor part 13 has a hinged arrangement with a hinge part 13b, and a threaded catch arm 130. The thread shaft of arm 13c is rectangular to fit rectangular holes in hinge part 13b, so the arm cannot turn.

The eifective length of the arm 130 is varied by the draftsman to allow the clamp to lit the width of his T-square 2. This adjustment is. made by turning the threaded nut-like part 13g. The nut-like part 13g is tapped to suit the thread on arm 130, it has spaced holes around its perimeter for attaching the lever-like handle 13d. After the effective length of the arm 130 is adjusted to suit a particular Tsquare 2, the lever-like handle 13d is inserted in one of the spaced holes in part 13g. A thin resilient washer 13f around'the arm 13c prevents the nut 13g from creeping. The handle 13d is pivoted from right to left to tighten the clamp C1 and it is pivoted from left to right to loosen the clamp C1 in its relation to the T-square 2 to adjust for play. The handle 13d is pivoted to the extreme tightening position when it is desirable to tighten the clamp C1 to the T-square 2 so it will not slide which is useful in keeping the square Q positioned for drawing vertical lines longer than the leg of the square. The hinge arrangement formed by the protractor 13 and the hinged part 13b has a machine screw 13a. This machine screw 132 may be tightened with a screw driver when it is desirable to prevent any hinge action. As shown in Fig. 4, the non-threaded end of the arm 130 is beveled. This allows the arm 13c to engage the T-square 2 and the loose hinge action allows the arm 130 to rise and slide over top of the T-square 2, and then to drop to engage T-square 2 securely as shown. When the arm 130 is to engage the T-square 2, after sliding over top of it, the weight of the arm 13c and a loose hinge arrangement will allow the arm 13c to drop, and the hook-like end of arm 130 will bear against the T-square 2, preventing the protractor-clamp C1, etc., from disengaging in a lateral direction, thus locking the square Q in a position with the T-square 2, by means of this clamp or other combinations of the protractor-clamps C1, C2, C3, and C4. A slightly raised dot-dash outline of the arm 13c and the hinge part 13b, shown in Fig. 4, shows the elevated positions of these parts when they are sliding across the top of the T-square 2. The protractor clamps C1, etc., are self-aligning when they move against the edge of the T-square 2, unless they are over degrees from their selected position. The arm 13c and the hinge part 13b together are raised up pivotally to slightly over 90 degrees to keep them disengaged from the T-square 2, when they are not wanted in play to clamp on to the T- square. This high raised position of the arm 13c and the hinged part 13b is shown by a dot-dash outline in Fig. 4. To raise the arm 130, the draftsman may insert his finger under the sloping end of the arm 13c and pull the arm 13c upwardly.

The index arm N1 as shown in Fig. 2 would at times prevent the full hinging action of the arm 13c and the hinge part 13b on clamp C3, as they would be blocked by the bracing wires 10a, 10b, and other parts of the index arm N1. When that condition occurs, the pin 5b maybe disengaged from the clamp C3 or the index arm N1 and the protractor-clamp C3, together, may be raised by inserting a finger or finger nail under the arm 13c and raising them and sliding to a disengaged position where the hooked end of the arm 13c cannot engage the edge of the T-square 2. When this blocking condition occurs, the screw 132 may be tightened to prevent hinging action, and the arm N1 may be lifted, which will lift the clamp C3 also.

The raised strip 20 along the full length of the T-square 2, only a fragment is shown in Pig. 2, may be used on a T-squareor straight edge, which is tapered in width or it is too wide to be practical for clamping across its width. The raised portion of a so called draftsmans parallel edge, that is a rigged straight edge with a system of pulleys and cables to keep it in alignment, may be clamped onto in place of a raised strip 20. p

The clamp C4 may be disengaged and pushed aside when it is not being used, or the clamp C2 may be switched to the position of the clamp C4, if it is not being used on the arm 4a, thus eliminating a-clamp. Thus, when the engineering draftsman wants to keep the weight of the square Q to the minimum, this switching arrangement is used. If weight is no problem, or if it is preferred, a clamp C4 may be used while the clamp C2 is left on the arm 4a.

The square Q may be used with a curved edge guide, such as a draftsmans railroad curve template, to facilitate measuring and drawing radial lines and the like in sketching cambered or arched structural members and the like.

Thus there are many advantages to be had by using this square Q rather than some conventional tiltable or protractor-like instruments of limited use, since with this device the draftsman, etc., can index for and maintain accurate groups of angles or slopes, and he can reciprocate, push, or place the square Q into positions, where it is held by the T-square 2 to prevent it from tilting out of the selective drawing position, and where he can measure two ways and draw two lines with one positioning, whereas with most conventional drafting machines, this cannot be done easily since those machines cannot be anchored or be held accurately, and the scales are not generally made to come together at the center or to be quickly interchanged, and the machine must be shifted for every measurement and every line that is to be drawn.

In general with the present device, the draftsman can by proper procedure in drawing, scale as he draws without taking more time than he would for unscaled drawing. The ease of positioning the square Q, the ease of main taining a position, and the fewer positions required, are aids in maintaining speed and accuracy while drawing.

Drawing instruments other than the L-shaped squares, particularly edge guides, may be equipped with protractors and/ or clamps such as clamp C1 or clamp 2911, index arms such as arm N1, and interchangeable scalessuch as scale assembly S1.

A'u shaped graphic guide device, similar to that formedby placing two squares Q toe to toeand fastening them together, may be made similar to square Q. It wouldihe more cumbersome, but it does not require as much movement by the worker. It would beuseful in some branches of drafting.

Afull square shaped graphic guide device may be made similar to an L-shaped square with index arms, protractors, clamps, and interchangeable scales.

Figure 14 shows a modification similar to the arrangement shown in Fig. 1B. The square Q is clamped to the T-square 2, or other types of straight edges may be substituted. The square Q is supported by a swiveled arm 15, which is fastened to the board 1. This swiveled arm 15 is a triple hinged conventional device to support a load in various positions over a large area. The arm 15 is fastened to the ends of square Q with the same holes that are used to hold on the clips 7, or other suitable connections may be used. With this arrangement, the weight, or most of the weight, of the square Q may be carried by the arm 15; and thus it would take less effort for the workman to slide, rotate, or lift and move the square Q along the drawing surface. This arrangement may be used to lift the square Q slightly so that the operator could readily force the square to the working surface by slight pressure, or it may be adjusted to allow it to rest on the drawing while it is deflecting the arm 15 slightly with its weight, so little effort is required to lift it. The square Q is pivoted about a pin to get any of the desirable tilting positions that are required. This swiveled arm part attached to the square Q is shaped to counter-balance the square Q. The pivotable pin is at the center of gravity, so that the square Q remains at an approximate parallel plane from the working surface. The T-square 2, shown, has an adjustable head and a pin which projects into a metal grooved track near the left hand edge of the board 1. The T-square 2 can be tilted to other than 90 degrees from the so-called vertical edges of the board. This arrangement would allow making a sloping guide for the square Q. The head of the T-square 2 and the pin engaged in the groove restrain the T-square from moving laterally or tilting which makes it more useful in preventing the square Q from moving when it is clamped onto it.

Figure 15 shows another modification using an L-shaped square and the index arms N3a and N3b, which are identical in construction to the index arm N1. The index arms N3a and N3b are attached to hinges fastened onto the scaled legs 16a and 16b of a conventional drafting machine 16. The drafting machine 16 is a conventional device for measuring and drawing lines at various angles; it has a hinge which is connected to the drawing board 1a. This machine 16 always gives an angle and its complementary angle, as does the square Q. A protractor 160 has a clutch which allows the parts which form an L-shaped square similar to the square Q to be variably tilted to suitable positions for measuring and drawing. The pin indexed on the arm N311, the narrow mark 16e on leg 16b, or the outside center corner 16d of the square may be made to bear against one of the points 170 on the top edge of hinged straight edge 17a, located at the bottom of the board 1a, or a similar edge 17b at the side of the board. The edges 17a and 17b are hinged so that they may be raised above the surface of the board In to form a bearing surface with its edge to allow the pins on the pivot arms N3a and N3b to bear against it, to thus enable the draftsman to quickly and accurately adjust the drafting machine 16 to a selected tilted or horizontal position. When the tilting angle has been set, the machine 16 is pushed up on the board 1a and the straight edges are pivoted down to the project above the working surface of the board 1a. This hinging of the edges 17a and 17b allows the scales of the drafting machine 16 to project over the edge of the board la without them fouling the edges 17a and 17b scales 16a and 16b is longer than the distance from the outside center corner of the square to the arrow marks 16c and 16f on the legs 116a and 1615. Thus this square diifers in proportion to the arrangement for the square :Q. The edges 17a and 17b are used only for the quick accurate setting of selective angles or tilting positions of the machine 16. The index arms -N3a and N3b have protracto'rs 13, but no clamping parts are needed. The protractor 16c may be used to set the square formed by the scales 16a and 16b at various angles, but it is not indexed to allow intermittent interchanging of the various odd angles, only 0, 45 and 90. Each time'a new angle is used, it has to be reset accurately, whichtakes considerable time and effort. The protractor 160 is proportionately much smaller than the index arms N3a *a'nd N3b, in allowing-accurate setting of a desirable angle or tilt. The arrangement shown in Fig. 15 allows "the use of small low weight index arms.

Either index arm N31: or arm -N3b and their supplementary parts may be omitted, or only one arm such as arm N311 may be used and it may be switched with supplementary parts to the position shown for arm N3b.

Figure 16 shows a modified use of the square Q. A conventional drafting machine 18, which is similar to the machine 16, is hinged to the board 1b. A conventional protractor 18b on the machine 18 has a support 18a at tached. This support 18a may be pivoted around the protractor 18b. A modified L-shaped square QL is made up of a square Q, with the leg extensions Na and 19b attached by means of the holes used for the clips 7 and the arm 15. The clips 7 are moved out to the ends of the legs 19a and 19b, and longer scales, similar to scales S1 and S2, are attached. The square QL is used similar to the L-s'haped square formed by scales 16a and 16b, as shown in Fig. 15. The square QL has an index arm N4, which is similar to index arm N1. The end pins are arranged the same as for square Q, to allow indexing of selected angles. The index arm N4 and the pins 511 and 'S'k may have protractor clamps C1, to allow clamping of the square QL to the short straight edge of support 18a. This straight edge of support 18a works in a similar manner to the straight edge 17a. It allows the indexing of an angle, at the same time allowing the long legs of the square to project past the plane of the straight edge. Both legs of square QL may have hinges and pin arms to allow inter changing or additional clamps, and index arm to engage the straight edge on the support 18a. This square QL would be suitable for drawing long lines. This arrangement would enable the use of the short index arm N4 which would not be cumbersome. The extension legs 19a and 1% may be made in various suitable lengths. The index arm N4 may have the hinge 8e, as shown in Fig. 6, locked by advancing the pin 8g into the hinge parts. This locking of the hingeconnection would create a stiff index arm N4 to help support the square QL from the support 18a. Thus, when the knob on the protractor 18b is lifted, the square QL attached to the support 18a would be lifted also.

Figure 17 shows a modified graphic device which has an L-shaped square QS which is similar to the square Q. The legs 20a and 20b are conventional interchangeable drafting machine scales. The diaphragm 21 has grooves which fit the clips on the ends of the legs Zita and 20b. The index arms N5 and N6, which are similar to index arm N1, are fastened to suitable hinges attached to the legs 20a and 20b. The end pins 5m may be suitably attached to the and clips on the legs 26a and Mb. Protractors and/ or clamps may be used.

Figure 18 shows a modified graphic'device which has a positions shown by dot-dash outlines, so that they will not Square Q Which is Similar to the Squares Q and Q The legs 22a and 22b are conventional interchangeable drafting. machine scales, and they are similar to legs 20a and 20b. A diaphragm 23 is similar to diaphragm 21. The diaphragm 23 has legs 23a and 23b which have hinge when they are used in their areas. The square formed by connections for index arms N7 and N8. The ends of legs 23d and 23b have ofisets for suppo'rting endpins that are similar to pins a and 5a. Protractor-clarnps, or other clamps as described for square Q, may be used with modification. The squae QR has smaller index arms than does the square QS, but the same length scales as the square QS.

Figure 19 shows a modification which is a single straight edge SS. It has scale markings. It has a typical index arm N9, and it may have end pins similar to the pins 5a and 5c. Protractor-clamps, or other clamps as described for square Q, may be used. The tiltable straight edge SS may be used for measuring and drawing lines at various planes, similar to the method described for using the square Q, or it may be used in other ways. It may be used to hold conventional triangles in a tilted position so as to allow the drawing of a sloping line complementary to the slope at which the edge of the straight edge SS is set. The edge SS may be used in conjunction with a square CQ, which may be similar to a carpenter square, with markings along the edges of both faces. The square CQ may have a dove-tailed groove in its edges to engage the dove-tail shaped heads of pins 24. The pins 24 may be threaded into tapped holes in edge SS when they are to be used. Wtih this arrangement, the square CQ may be slid against the face of the edge SS to thus hold the square at various indexed angles for measuring and drawing on drawings or on material which must be marked for fabrication, such as lumber, sheet metal, etc. When the edge SS is used as a guide for marking lumber, structural steel, etc., modified pins, similar to pins 5a and 50 but longer so they may be projected down to engage and bear against the edge of the member being layed out, are used. These long modified pins may be strongly magnetic to make them stay in contact with a structural steel member or a steel straight edge.

Figure 20 shows a modified L-shaped square. It has a body 31, which may be of transparent plastic. It may have scale graduations along its edges. It has permanent magnets 29d, 29e, and 29f attached to the body 31. These magnets are used as are magnets 29a, 29b, and 29c in the square Q to act as clamps to hold the square to the edge of a T-square that has iron in it. Any one or any two of the magnets 29d, 2%, and 29 may be omitted to make cheaper squares that have more limited usefulness. The square may be flopped over as both faces are usable.

Figure 21 shows a modification in the form of a triangle. Its L-shaped square part is similar to the square shown in Fig. 21. The triangle has a body 32, which may be of transparent plastic. It may have scale graduations along its edges. It has permanent magnets 29g, 291:, and 2% attached to the body 32. These magnets are used, as are magnets 29a, 29b, and 29c in the square Q, to act as clamps to hold the triangle to the edge of a T-square that has iron in it. Any one or any two of the magnets 29g, 29h, and 291: may be omitted to make cheaper triangles that have more limited usefulness. The triangle may be flopped over as both faces are usable.

The graphic L-shaped squares and the like that have been previously described may have modified pins similar to pin 511, but longer so they may be made to project below the working plane to be drawn on. These modified long pins may be magnetized so they may act as magnetic clamps when they are made to bear against a metal edge with iron in it, particularly in the reverse bearing direction from that shown in Fig. 2 to the T-square. This arrangement would allow these graphic devices to be clamped onto a steel plate and the like, so as to use it to help mark layout lines on the plate and the like.

Thus it will be seen that I have provided an economical and eflicient graphic equipment capable of performing a wide'variety of operations to suit conditions.

While I have illustrated and described several embodia ments of my invention, it will be understood that these are by way of illustration only, and that various changes and'modifications may be made-within the contemplation d6 of my invention and within the scope of the following claims.

I claim:

1. A drawing instrument comprising an L-shaped square having graduations along each leg, a straight edge, said square being tiltably mounted with respect to said straight edge selectively about two bearing points spaced along one leg of said square, only one of said bearing points engaging said straight edge when the said square is tilted, said square having a straight indexing arm attached to an intermediate portion of said leg, said indexing arm having a retractable pin equidistantly spaced from said bearing points, said pin being engageable with said straight edge and being adjustable on the indexing arm to vary the distance between said square and said straight edge for selectively tilting the square relative to the straight edge, said square being tiltable in opposite directions by selectively engaging the said bearing points and said pin on said straight edge to obtain opposite sets of sloping positions for the legs of said square to allow the drawing of sets of lines ninety degrees to each other and oppositely sloped, said retractable pin being retractable away from said straight edge to allow both of said bearing points to engage said straight edge simultaneously to position the said square into a non-tilted position to permit non-sloping lines to be measured and drawn at right angles to each other along the edges of the said square. I

2. A drawing instrument comprising an L-shaped square having graduations, a straight edge, said square being mounted for tiltable movement with respect to said straight edge, said square having an indexing arm secured to an intermediate portion of one side thereof and adjustably clamped to said straight edge, there being a threaded rack for receiving a retractable pin for selectively coupling or uncoupling said square and straight edge along a plurality of points on said rack and therefore predetermining the angle of tilt of said square relative to the straight edge.

3. A drawing instrument as recited in claim 2 wherein said indexing arm is secured to said square at the mid point of one side thereof and wherein opposite ends of said side of said square are pivots whereby said square may be tiltable either at the intersection of its arms or at one extremity of an arm.

4. A drawing instrument comprising an L-shaped square having graduations, a straight edge, an indexing arm secured to an intermediate portion of one of the legs of said square and including a clamp for clamping saidindexing arm to said straight edge and preventing tilting movement therebetween, said square having a clamp at one of the extremities of said one of the legs of the square for clamping to said straight edge so as to maintain the angle of tilt of the square and at the same time permit sliding movement of the square at the tilted position with respect to the straight edge.

5. A drawing instrument as recited in claim 4 wherein two clamps are provided on said square, one at the junction of the two legs and the other at the extremity of the said one of legs, whereby either extremity may be clamped in position to said straight edge.

6. A drawing instrument comprising L-shaped square having graduations, said square having a plurality of clamps, one clamp at each of its extremities and one clamp at the junction of the two legs, said clamps being selectively clamped to said straight edge, an indexing arm secured'to the base leg of said square centrally thereof, said indexing arm including a clamp for clamping thereof to said straight edge, whereby the distance between the straight edge and point of connection of the indexing arm to the square may be varied.

7. A drawing instrument as recited in claim 6 wherein said indexing arm is detachably secured to said square, and wherein the other legof said square has fastening means whereby the indexing arm maybe transferred from one leg to the other of said square.

8. A drawing instrument comprising an L-shaped square, a straight edge, said square having an indexing arm secured to an intermediate part of one of its legs, said indexing arm being clamped to said straight edge, and means for adjusting the distance between the point of connection of the indexing arm to the square and the straight edge, said means comprising a worm and rack in threaded engagement therewith, means for detachably coupling and uncoupling said worm with respect to the rack, and means for securely fastening said worm in any selected position, so that at the selected position the worm may be turned with respect to the rack to obtain Vernier adjustment, and retractable pin means for selectively coupling and uncoupling said indexing arm with respect to said straight edge.

9. A drawing instrument comprising an rL-shaped square having graduations, a straight edge against which said square is tiltably mounted, said square having clamps at the extremities of its base leg, said clamps being self coupling with respect to to the straight edge when the particular extremity on which the clamp in located is moved against the straight edge, an indexing arm fastened at a point equidistant between said extremities of the base leg and being selectively clamped to said straight edge at selective distances between the straight edge and the intermediate portion of the base leg, whereby preselected angles of tilt of said square relative to said straight edge may be obtained.

10. A drawing instrument as recited in claim 9 wherein each of said clamps includes protractors, whereby the angle of tilt of the square relative to the straight edge may be readily measured.

11. A drawing instrument as recited in claim 9 wherein at least one of said protractors includes two pointers disposed at 90 degrees relationship for cooperation with difierent portions of the scale of the protractor.

12. A drawing instrument comprising an L-shaped 4 square, a straight edge, pivotal means at opposite extremities of one of the legs of said square for pivotal movement with respect to said straight edge, an indexing arm having one end secured to an intermediate portion of said one of the legs and being clamped to said straight edge, retractable pin means for selectively coupling or uncoupling said indexing arm to said straight edge to allow either predetermined tilting of said square relative to said straight edge by coupling of said pin means, or coincidence of said one of the legs and straight edge after uncoupling of said pin means to permit relative sliding movement.

13. A drawing instrument as recited in claim 12 wherein a plurality of retractable pin means are provided at spaced points along said indexing arm to permit selective angular tilting movements of said square relative to said straight edge, whereby said square may be quickly moved and indexed to a plurality of angular positions with respect to said straight edge or in coincidence therewith merely by uncoupling and coupling of said pin means.

References Cited in the file of this patent UNITED STATES PATENTS Re. 11,189 Carr Sept. 15, 1891 458,606 Weaver Sept. 1, 1891 500,727 Walentowitz July 4, 1893 965,483 Noyes July 26, 1910 1,382,460 Berglof June 21, 1921 1,459,792 Nilant June 26, 1923 1,909,289 Little May 16, 1933 2,136,140 Langsner Nov. 8, 1938 2,307,584 Harris Jan. 5, 1943 2,568,575 Wickman Sept. 18, 1951 FOREIGN PATENTS 239,397 Germany Oct. 13, 1911 126,838 Switzerland July 2, 1928 952,708 France May 9, 1949 OTHER REFERENCES Emmert publication, Emmert Manufacturing Co.,

0 Waynesboro 2, Pa., Bulletin No. 6-48, received in the US.

Patent Ofiice June 13, 1952. 

